1. Field of the Invention
The present invention relates to an antenna system, and in particular to a glass antenna system for a vehicle windshield having a connector with an integral impedance matching network to optimize the performance of the glass antenna.
2. Technical Considerations
In the past, the traditional motor vehicle antenna for receiving and transmitting electromagnetic signals was a mast or whip-type antenna. Recently, there has been a trend towards incorporating the antenna into the vehicle structure. For example, U.S. Pat. No. 3,987,449 to DeAngelis et al. discloses a wire antenna laminated within a vehicle windshield. U.S. Pat. No. 4,707,700 to Nagy positions an antenna within the roof structure of a vehicle. U.S. Pat. No. 5,416,491 to Nishikawa et al. forms antenna elements on a window using electro-conductive ceramic paints. U.S. Pat. Nos. 4,768,037 and 4,849,766 to Inaba et al. and 5,355,144 to Walton et al. use a transparent electroconductive coating laminated between two glass plies to form the antenna.
In designing an antenna system, attention is given to matching the impedance of the system components, and in particular matching the impedance of the radio, the antenna and the feedline between these two components. This is a critical issue for the performance in FM reception since impedance mismatch results in significant loss of signal. Further complicating the antenna system design is the fact that the impedance of the antenna component of the system may vary substantially over the FM frequency band. This means a simple impedance match, such as a single capacitor, will not address the overall performance issues for FM reception over the entire frequency band.
In a glass antenna, the impedance of the antenna is typically not well matched to the radio and the feedline. One way this issue has been addressed by antenna designers is to design the antenna to have a desired impedance, for example, as disclosed in U.S. Pat. Nos. 5,083,135 and 5,528,314 to Nagy et al. Designing the antenna to a predetermined impedance improves the antenna performance but as discussed above, the impedance generally varies over the FM band based on frequency so that the antenna design may not be optimal over the entire FM frequency band. In addition, designing the antenna to have a predetermined impedance would require each antenna to be designed specifically for the particular type of radio and feedline in the particular antenna system as well as the vehicle into which the windshield is installed.
It would be advantageous to provide a glass antenna system for a vehicle which provides improved performance, in particular for the FM frequencies, without having to redesign the antenna system based on the vehicle and/or types of components used in the system.